This invention relates to improved coating compositions based on monovinylidene aromatic, conjugated diene and acid monomers further comprising an emulsifying, sulfoalkyl monomer polymerized therein. Preferably, these are latexes prepared by an aqueous dispersion polymerization process.
Latexes or aqueous dispersions of polymers of monovinylidene aromatic and conjugated diene monomers find wide spread usage as coating materials, particularly in the area of paper coatings. It is well known in the art that emulsifiers or surfactants must be added to achieve stable, aqueous dispersions of these polymeric materials. However, such additives tend to cause foaming problems in the latex production process and to reduce the moisture resistance of the coatings that are prepared with the latex polymers. It is also known that certain monomers having hydrophilic moieties can be used in preparing the polymer and will assist in emulsifying and stabilizing it in an aqueous dispersion. See, for example U.S. Pat. No. 3,033,833 and GB 2,175,594. In these references sulfoalkyl monomers are used to prepare latex polymers. It has been found, however, that the polymers of the type described will typically decrease in moisture resistance if the latex stability is improved and vice-versa. It has also usually been found that when used in paper coating formulations, improvements in wet pick resistance are only obtained with an accompanying loss of dry pick resistance or vice versa.
It is an object of the present invention to provide polymer compositions based on monovinylidene aromatic and conjugated diene monomers which have good stability in aqueous dispersion form and have good adhesion to substrates and/or fillers under conditions of impact and shearing forces, even in the presence of moisture. When such polymers are used in paper coatings these qualities are particularly important and provide the coating with good resistance to wet and dry "picking" of the paper coating. It is another object to provide aqueous polymer dispersions suitable for use in preparing paper coating formulations having the above desirable properties. It is a further object to provide the paper coating formulations, paper coatings and coated paper articles that can be prepared.